San Francisco police were digging into the past of a United Parcel Service employee as they tried to figure out why he allegedly killed three co-workers at a company distribution center before shooting himself to death Wednesday.

Investigators did not immediately name the suspect, saying they needed to confirm his identity. But they seized a BMW belonging to 38-year-old Jimmy Chanh Lam, which was parked near the shooting scene, and they raided Lam’s home in the Inner Richmond neighborhood, where neighbors said he mostly kept to himself.

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Workers at the UPS building at 320 San Bruno Ave. said the gunman was a fellow employee, and Assistant Police Chief Toney Chaplin said the shooter was wearing a UPS uniform. Lam’s neighbors said they often saw him walking around in a company uniform, looking at his phone and smoking a cigarette.

According to a Union official, the gunman had filed overtime grievance.

In the afternoon, officers left his home — one of two units in a grayish green building — with what appeared to be a computer, several bags of evidence and a file box. Around the same time, police towed away a black 2012 BMW Coupe registered to Lam that had been parked near the shooting scene.

“I’m a little creeped out,” said Jennifer Plog, who lives next door to Lam’s home and said he had appeared harmless. “It’s creepy knowing that people next door have the ability to have guns and shoot people they work with. It makes me feel unsafe.”

No one interviewed in the neighborhood of two-story homes and apartments said they had spoken with Lam. They described the street, just around the corner from a bustling corridor of restaurants, as the kind of place where neighbors recognize each other but don’t necessarily talk or know each other’s names. And Lam was quiet.

According to court records, Lam’s only brushes with the law involved driving. In 2010, he was convicted of driving under the influence and was placed on probation after San Francisco police said he crashed into parked vehicles. He allegedly had neither a valid license nor insurance.

Three years later, city prosecutors filed a motion to revoke his probation when he was arrested again for driving under the influence.

Police officials said they recovered two guns from the scene of the shooting, including what they described as an assault pistol. They did not provide further details or say where the guns had come from or whether they had been legally purchased.

The shooting happened at 8:55 a.m. as UPS workers gathered for a regular meeting called “Wednesday Wellness,” causing panic as employees dived to the ground or ran for safety. In addition to killing three, the gunman wounded at least two others, while three people were injured while fleeing, officials said.

When responding police officers encountered the suspect inside the building, officials said, he raised a pistol to his head and pulled the trigger.